1. Field of the Invention
The present invention relates generally to kinematic mounts and particularly to an apparatus for removably coupling two plates to one another, such that despite repeated disassembly and reassembly the plates remain in identical positions when reassembled.
2. Description of Related Art
Kinematic mounts, otherwise known as kinematic couplings or restraints, are commonly used to couple measuring equipment or instruments (instrument/s) to a base or substructure, where despite repeated disassembly and reassembly the plates remain in the same relative position to one another as when previously assembled.
Examples of such instruments include: precision instruments, such as optical elements, including lenses mirrors, prisms, telescopes, cameras, lasers, sensors, or the like; sensitive measuring equipment; strain sensitive devices; lithography equipment, such as projection optics; and instruments that are disassembled and moved frequently so that a permanent support is not suitable.
Indeed, very small changes in the position of such instruments can make a substantial difference in the accuracy of results obtained from the instrument. Therefore, kinematic mounts were developed to address such precise repeated assembly.
According to well-known principles, for a rigid body to be completely fixed in space, despite repeated disassembly and reassembly, all six degrees of freedom need to be constrained. In other words, three translations and three rotations must be constrained with respect to some arbitrary fixed coordinate system. A mount is said to be kinematic when all six degrees of freedom are constrained without any additional constraints, i.e., any additional constraints would be redundant. A kinematic mount therefore has six independent constraints.
One well-known kinematic mount includes a fixed base plate which has three V-shaped grooves formed therein. Each groove forms an angle of approximately 120 degrees with each other groove, and the walls of each groove form angles of approximately 45 degrees with the surface of the base plate. On a second plate, three convex spherical members are secured roughly in an equilateral triangular array. When the second plate is rested upon the first plate, each of the three convex spherical members rests within one of the three grooves, contacting the two side walls of each respective groove at two point contacts. Any instrument secured to the second plate, which may be lifted from the base plate and, when replaced, will occupy the identical position relative to the base, which normally remains fixed.
However, the above described point contacts between each spherical member and groove leads to concentrated forces at these contact points. These concentrated forces lead to high stresses, known as Hertzian stresses, both at the spherical member and at the groove.
The above described mount, while being sufficient for light loads, such as laboratory applications or light-duty field applications, fails in heavy-duty applications, such as when used in space launch vehicles, where high intensity vibrations and shocks cause failure at the point contacts.
In light of the above it is highly desirable to provide a kinematic mount that addresses the high stresses generated by point contacts, while still providing a kinematic mount, as described above.
According to the invention there is provided a kinematic mount for repeatedly coupling two components together. The kinematic mount preferably includes a first plate, a second plate, and three connectors. The first plate has three indentations therein, where the indentations are each located at respective apexes of an equilateral triangle and are preferably conical indentations. The second plate has three grooves therein, where the grooves are spaced about 120 degrees apart from one another. Each connector comprises a first surface and a second surface. The first surface forms an annular contact line between the first surface and one of the indentations. The second surface is coupled to the first surface and defines two substantially parallel contact lines between the second surface and one of the grooves. In a preferred embodiment, the first surface defines a spherical surface and the second surface defines a cylindrical surface. A center of a sphere that defines said spherical surface substantially coincides with a centerline of a cylinder that defines said cylindrical surface.
This kinematic mount provides increased stiffness and repeatability under high loads.